I recently changed my 2L diesel (45mpg, £180.00 pa tax) for a 1L petrol (38mpg, £30.00 pa tax). How can this be right?

It was a blip, I did the same but with the opposite effect, 2l diesel, £30 tax to 1l petrol, £140 tax.
The recent tax changes have started (who’d have seen it coming! ) to swing the pendulum back in favour of the gummint once again.

Because mathematically, and under test conditions it produces less CO2 per kilometre driven than you old diesel. NOX output is also lower which I think affects the tax band for petrol Vs diesel.

We have a 1.4 Corsa (petrol) which is supposed to do around 58 MPG overall, but it struggles to do 40 MPG except on a very long run. Apparently this is quite normal.

Thanks Nigel. Mathematically and under test conditions says it all!

I must admit I was hoping for rather more than 38mpg but taking into account the lower tax and lower fuel price I probably won't be any worse off. Until they think of some other way they can justify to make us pay more for choosing not to use the public transport that isn't available...…

__________________John

"A hundredth of a second here, a hundredth of a second there — even if you put them end to end, they still only add up to one, two, perhaps three seconds, snatched from eternity." ~ Robert Doisneau

I must admit I was hoping for rather more than 38mpg but taking into account the lower tax and lower fuel price I probably won't be any worse off. Until they think of some other way they can justify to make us pay more for choosing not to use the public transport that isn't available...…

Driving patterns have a big effect on fuel economy; possibly even more so than driving style.

Our little Corsa is seemingly up to temperature within about three or four miles, but the MPG is poor unless we use it for much longer journeys; which is not what most people buy a Corsa for really.

My wife drives almost exactly ten miles each way to and from work on mostly main-ish roads. Traffic is not usually a problem, but overall MPG is rarely better than 40 MPG. However, when we have used the car for much longer journeys (100 miles plus) it will return 50 + MPG.

There are a couple of things you might like to try. Firstly we find that Esso and Shell unleaded provides a good 2 - 4 MPG improvement over supermarket fuels. Secondly, a dose of Redex in each tankful also seems to help. It only had 6,000 miles on the clock when we bought it, and 20,000 miles now, so it is still virtually new.

Our daughter 'inherited' our old 1.6 16V Mk V Astra, which like the Corsa struggled to do 40 MPG, although it is a bigger, heavier car with a more powerful engine. However, with a dose of Redex added to Shell Regular Unleaded it manages 46 MPG overall, with 50 MPG on the long runs to university and back.

(Wilco usually sells Redex for £2 a bottle. Tesco also have offers on it from time to time.)

You might also look into having the engine re-mapped. Apparently much of the problem is that fuelling of petrol engines is not individually tuned, but rather the ECU is set to 'safe' air/fuel mixtures, which means that rather more fuel is injected than is needed. (Lean mixtures tend to run much hotter, but overly-rich mixtures waste fuel and cause flat-spots.)

I have been quoted around £200 to remap the Cora, which is claimed to iron out the many flat spots and provide at least 10% improvement in fuel economy. It seems like a lot of money to pay but at £60 for a tankful of unleaded.

Diesel engines can also benefit from remapping but I am more circumspect about that.